I honestly like ones that keep the plot in the description/book itself. Ones titled things like "Vampire Kisses" and have two people making out on the front cover isn't that interesting to me. But, say, with The Fault in Our Stars door John Green, I like it because you'd never guess it was about terminal cancer (I also like it because it was door John Green, but that's not the point). Quirky titles and covers just draw me in. I know that's 'judging a book door its cover', but a good cover design/title can change the whole feeling of a book.
((WARNING: Be prepared for weirdness) Well, when I walk into a bookstore/library, I always have a vague idea of what I want. I learned early on that that helps me find it faster. I feel a sort of pull towards what I'm looking for. Sometimes, I'll be puled to boeken I already know, but I was pulled there because they are familiar. I never wander around. If I'm pulled to a certain shelf, I'll scan ths tirles, searching for the one that pulled me. If it looks promising, I'll take it off the shelf and read the back. meer often than not, I end up putting the book back.
Not always the titel of the book, of the book cover. Because the author/illustrator doesn't have to be artistic. Like me, I'm personally NOT an artist.
Usually if the plot is mysterious and exciting, if it catches my attention, I go for the book. Usually, I like reading dystopian fiction, like maybe if the character has unusual traits, I figure that the book is probably good. Like this book.